1. Field of the Invention
The present invention relates to an apparatus for fabricating semiconductor devices, and more particularly, to an apparatus for fabricating semiconductor devices using plasma.
2. Description of the Related Art
As the integration of semiconductor devices increases, the demand for a deposition technique to form a material film having a uniform thickness, or an etching technique showing a uniform etch rate also increases. Accordingly, a plasma apparatus for depositing a material film or etching the material film by appropriately controlling the type of ions and ion energies is being widely used for the manufacture of highly-integrated semiconductor devices. To be more specific, the plasma apparatus can be applied to dry etching, chemical vapor deposition (CVD) or sputtering techniques.
Meanwhile, a radio frequency generator is widely used as an energy source for generating the plasma used in these techniques.
FIG. 1A is a schematic of a conventional plasma apparatus, and FIG. 1B is a plan view of the chuck and the gas injection ring shown in FIG. 1A.
Referring to FIG. 1A, a chuck 5 is installed on the bottom of a chamber 10, which has an opening at the top, and a chuck support 15 made of an insulating material is interposed between the chuck 5 and the bottom of the chamber 10. A wafer on which a semiconductor device is to be formed, is loaded on the chuck 5. A gas injection ring 20 is installed around the sidewall of the chuck 5, and is fixed by a fixing means 25 such as a bolt in contact with the bottom of the chamber 10. The gas injection ring 20 is preferably attached in such a way that it is electrically connected to the chamber 10, which has a ground potential. The chuck 5 and the gas injection ring 20 are spaced apart from each other by a predetermined interval, for example, at an interval of about 1 to 5 mm. Thus, a gap exists between the chuck 5 and the gas injection ring 20, such that the gas injection ring 20 and the chuck 5 form a chuck capacitor.
The sidewall of the chamber 10 or a predetermined area of the bottom of the chamber 10 is branched and connected to a vacuum pump 30. The opening of the chamber 10 is covered by a cover 35, which is formed of a dielectric material. An electrode 40 connected to a first plasma power source 45a for generating radio frequency power, is installed over the cover 35. Thus, when the first plasma power source 45a is turned on, plasma is generated within the chamber 10.
A first radio frequency matching circuit 50a for maximizing the transmission efficiency of radio frequency power generated from the first plasma power source 45a is interposed between the first plasma power source 45a and the electrode 40. The chuck 5 is connected to a second plasma power source 45b, which is used to induce plasma generated within the chamber 10 by the first plasma power source 45a over the chuck 5.
A gas injection passage for supplying process gas into the chamber 10 is installed within the gas injection ring 20. The gas injection passage is connected to a tank 55 which contains a gas source, via a gas inlet. A second radio frequency matching circuit 50b having the same function as that of 50a is interposed between the second plasma power source 45b and the chuck 5. A valve 60 for controlling the flow of gas is installed at a predetermined position on the gas inlet between the tank 55 and the gas injection ring 20. The valve 60 and the pump 30 are controlled by a valve control signal .PHI..sub.v and a pump control signal .PHI..sub.p, respectively, which are generated from a system controller 65 that controls the operation of the plasma apparatus. The system controller 65 receives signals from the first and second plasma power sources 45a and 45b and detects an on/off state of each of the first and second plasma power sources 45a and 45b.
As described above, the total chuck capacitance between the chuck 5 and a ground terminal is directly affected by the change in chuck capacitance between the chuck 5 and the gas injection ring 20. Thus, when the chuck capacitance is changed, the total chuck capacitance is also changed. The total chuck capacitance in turn directly affects a plasma process. This means that when the total chuck capacitance is changed, the sheath potential between the chuck 5 and the plasma induced over the chuck 5 by the second plasma power source 45b is changed. When the sheath potential is changed as described above, process parameters for the plasma process are changed. For example, the process parameters are an etch rate, a deposition rate or the like. Hence, the total chuck capacitance between the chuck 5 and the ground terminal must be kept constant to obtain excellent process uniformity.
Meanwhile, the plasma apparatus must be periodically pre-maintained as are other apparatuses used to fabricate semiconductor devices. This pre-maintenance is required since another factor that changes the process parameters is generated by the absorption of a contaminant on the inner wall of the chamber as the process time or the frequency of processing increases. Thus, the plasma apparatus must undergo a pre-maintenance operation of disassembling the plasma apparatus, cleaning the respective component elements including the chamber, and reassembling the disassembled component elements. During the pre-maintenance operation, an operation involving measuring and controlling the gap between the chuck 5 and the gas injection ring 20 using a gage or the like, is performed several times to adjust the gap to within an allowable range. This operation is manually performed, requiring a great amount of time to perform, and making it difficult to accurately adjust the gap to within the allowable range. As a result of this, when the chuck 5 and the gas injection ring 20 are assembled such that they do not have the same center as shown in FIG. 4B, a first gap G.sub.1 on the left side of the chuck 5 and a second gap G.sub.2 on the right side of the chuck 5 can be different. In other words, the gap between the chuck 5 and the gas injection ring 20 may not be the same at all positions around the chuck 5. When the gap between the chuck 5 and the gas injection ring 20 is not uniform as described above, the chuck capacitance may exceed an allowable range. Accordingly, as the total chuck capacitance changes, the uniformity of the process can be degraded.
While a process gas is sprayed into the chamber 10 via the gas injection ring 20, a physical force due to the pressure or the like of the process gas, is applied to the gas injection ring 20. In addition, minute vibrations can be generated in the plasma apparatus when it is used for a long time. Thus, even when the gas injection ring 20 is fixed to the chamber 10 by the fixing means 25, the position of the gas injection ring 20 can change when the plasma process is performed for a long time. When the position of the gas injection ring 20 changes as described above, the gap between the chuck 5 and the gas injection ring 20 changes. Accordingly, chuck capacitance changes, and the total chuck capacitance also changes.
As described above, the total chuck capacitance between the chuck 5 and the grounding terminal of the conventional plasma apparatus cannot be kept constant.